Concrete has an advantage of maintaining strength over a long period of time as a constructional material.
However, in a hot season such as summer, heat accumulates in the concrete due to the outside air, direct sun rays, etc., and thus the inside of a building is heated by the accumulated heat. In addition, in winter, the concrete cools the inside of a building.
Accordingly, insulation processing is usually performed on the concrete. For example, an insulating layer is formed by spraying hard polyurethane foam onto the surface of the concrete such as a rebar-reinforced concrete used in multiple dwelling houses such as apartments.
However, if the insulating layer is formed simply by spraying the hard polyurethane foam, the hard, polyurethane foam can burn easily in case of a fire in the building. Therefore, polyurethane foams that have a self-extinguishable or flame retardant property have been developed and are described, for example, in Patent Literatures 1 to 12.